A conventional variable-capacitance diode device that is used as a tuning device for high frequencies has a maximum capacity of 0.1 to 15 pF, for an area of its PN junction and an area of a conductor film for a wire bonding are extremely small. Usually, a wire of a thick diameter cannot be used to bond a single gold wire or the like to a single variable-capacitance diode device, so a thin wire is used for the small area of the wire bonding.